III-V compound semiconductor materials have applications for the formation of electronic devices such as field-effect transistors (FETs) and heterojunction bipolar transistors (HBTs) and the like; and for the formation of photonic devices such as vertical-cavity surface-emitting lasers (VCSELs), edge-emitting lasers, reflectance modulators, and the like. For many of these compound semiconductor devices, a precision etching is required for defining the device structure and/or electrically isolating adjacent devices. A dry etching method is to be preferred over a wet etching method due to being cleaner, having a greater repeatability, providing more anisotropic and higher-aspect etch profiles, providing an improved etch depth control and uniformity across a substrate or wafer, and allowing a smaller size of etchable structures. Dry etching is also independent of surface orientation, allowing the formation of substantially vertical etch sidewalls, even on misoriented substrates that may be preferred for the growth of some compound semiconductor materials such as InGaP and AlGaInP.
Compound semiconductor materials formed of one or more layers that include both aluminum and indium (e.g. AlGaInP or the like) have been particularly difficult to etch since both aluminum and indium tend to make dry etching result in a rough surface texture for the compound semiconductor material.
The present invention represents an advance over the prior art dry etching methods used heretofore for etching of compound semiconductor materials.
S. J. Pearton et al disclose the use of hydrogen iodide (HI) in combination with methane and hydrogen for electron cyclotron resonance (ECR) plasma etching of InP, InGaAs, InAlAs, InAlP, InAs, and InSb in an article entitled "High-Rate Anisotropic Dry Etching of InP in HI-Based Discharges," Applied Physics Letters, volume 60, pages 838-840, 17 February 1992. A disadvantage of such HI-based discharges are that they are known to be extremely corrosive.
T. Yoshikawa et al disclose dry etching of AlGaInP in a chlorine reactive ion beam apparatus in an article entitled "Smooth Vertical Etching of AlGaInP by Cl2 Reactive Ion Beam Etching," Electronics Letters, volume 29, pages 190-192, 21 January 1993. Yoshikawa et al disclose that any residual water vapor in the etching chamber can oxidize the Al resulting in retarded etching and a rough etched surface. For this reason, a lengthy preparation time (over 8 hours) was required for evacuation of the etching chamber (to 4.times.10.sup.-8 torr) and baking of the chamber and gas lines prior to etching. Such a lengthy preparation time is disadvantageous in reducing throughput and thereby increasing manufacturing cost. Furthermore, the high chlorine ion beam energy of about 1 keV is disadvantageous in producing damage to the compound semiconductor material which is undesirable for many types of sensitive compound semiconductor devices.
S. S. Ou et al disclose dry etching of GaInP/GaAlInP surface-emitting laser diodes having 45.degree. and 90.degree. deflecting micromirrors by argon ion beam etching in an article entitled "635 nm GaInP/GaAlInP Surface-Emitting Laser Diodes," Applied Physics Letters, volume 63, pages 3262-3264, 13 December 1993. The use of an argon ion beam for etching GaInP and GaAlInP is disadvantages due to a low etching rate of only about 30 nm/minute, and also due to damage to the compound semiconductor material produced by the 0.5 keV energy of the Ar ion beam.
What is needed is a dry etch method that is capable of etching compound semiconductor materials containing aluminum, and/or indium while providing a relatively high etch rate of up to about 50 nm/minute or higher, and smooth etched surfaces with minimal ion bombardment damage.